Physiological and morphological evidence suggests that in skeletal and cardiac muscles the transverse tubules (T-tubules) play an important role in the mechanisms which trigger muscle contraction by release of Ca2 ion (excitation-contraction coupling). In order to understand the role of the T-tubule in excitation-contraction coupling it is essential to obtain better knowledge of the molecular nature of the components of the T-tubules and of the role they play. In order to attain this goal we will prepare purified T-tubule membranes and will characterize their biological function such as ATPase activities, calcium pumps and Na ion/Ca2 ion exchange systems. Antibodies will be prepared against the purified tubule fractions and used as probes to identify and isolate the molecular components associated with various T-tubule functions. Those involved in excitation-contraction coupling will also be identified by using specific antibodies on single fiber preparations. These antibodies will also be used for electron microscopic localization of T-tubule constituents in situ.